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        // console.log("内层变量覆盖外层变量");
        var a = 1000;
        
        function f(){
            console.log(a);
            if(false){
                var a = 'ni hao';
            }
        }

        f();//undefined

        // 2.4计数的循环变量泄露为全局变量
        var str = 'welcome';
        for (var i =0;i < str.length;i++){
            console.log(str[i]);

        }

        console.log(i);//7

        console.log("----------------");
        // 块级作用域
        function fun(){
            let n = 'a';
            if(true){
                let n = 'b';
            }
            console.log(n);//'a'
        }
        fun();
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